Modular fiber reinforced plastic enclosed bridge

ABSTRACT

A method for fabricating a fiber reinforced composite bridge module is described which in one preferred embodiment includes the steps of selecting a cross-sectional shape for the bridge module defined by an outer substantially tubular shell having a top side and a bottom side, and a floor deck near the bottom side and at least one keel beam beneath the floor deck and extending lengthwise of the outer shell, the outer shell, floor deck and keel beams defining a plurality of passageways along the length of the module, winding fiber and impregnating material on mandrels in a plurality tubular sections defining the plurality of passageways, joining the plurality of tubular sections in side-by-side relationship in an assembly substantially defining in cross section the cross-sectional shape of the module, winding fiber and impregnating material around the assembly to a preselected thickness for the outer shell; and curing the fiber and impregnating material.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

This application claims the benefit of U.S. Provisional No. 60/039,759filed Mar. 3, 1997.

BACKGROUND OF THE INVENTION

The present invention relates generally to structure and manufacture ofmodular bridges, and more particularly to modular bridge structurescomprising fiber reinforced plastic (FRP) composite.

Conventional pedestrian bridges have typically been fabricated of steel,concrete, and wood. Some composite bridge structures have been proposedbut use truss designs in which pultruded composite members are linkedtogether so that each member takes compression or tension similarly tocomparable steel construction. Certain composite vehicular bridgestructures utilize non-winding fabrication techniques, each structureconsisting of many individual parts all adhered or fastened together,which is very labor intensive during the fabrication phase. One suchstructure requires that truss-built sides be transported to the site andconnected with composite members that comprise the floor deck. Thebridge is built on site using standard assembly techniques, which may besatisfactory for standard building materials, but is marginal forcomposites. Because the structures can be fabricated only in part at afactory and must be assembled at the bridge site, substantial disruptionof traffic flow may result. Assembly techniques for the structures usemechanical fasteners which create points of stress concentration.

The invention described herein solves or substantially reduces incritical importance problems with previously existing bridge structuresand fabrication methods by providing an enclosed FRP composite bridgestructure that exploits the high specific strength and stiffness of FRPmaterials, has low fabrication costs, omits nonstructural wall and roofmembers that add unnecessary weight, has a minimum number of mechanicalfasteners and fewer sites for structural failure, is fabricated inmodules with various cross sectional configurations, can be factoryfabricated and assembled, thereby avoiding site weather conditions thathamper installation or compromise tolerances, and can be transported tothe site completely assembled or in modules and installed with minimaldisruption of traffic flow.

It is therefore a principal object of the invention to provide an FRPbridge structure and fabrication method.

It is a further object of the invention to provide an inexpensive,strong, lightweight and corrosion resistant bridge structure.

It is yet another object of the invention to provide an FRP bridgestructure that can be fabricated in modular form and assembled to adesired length.

It is another object of the invention to provide a factory fabricatedand assembled bridge structure for installation at a bridge site withminimal interruption of traffic flow.

It is yet another object of the invention to provide a bridge structurerequiring substantially lower maintenance during bridge lifetime ascompared to previously existing bridge structures.

These and other objects of the invention will become apparent as adetailed description of representative embodiments proceeds.

SUMMARY OF THE INVENTION

In accordance with the foregoing principles and objects of theinvention, a method for fabricating a fiber reinforced composite bridgemodule is described which in one preferred embodiment includes the stepsof selecting a cross-sectional shape for the bridge module defined by anouter substantially tubular shell having a top side and a bottom side,and a floor deck near the bottom side and at least one keel beam beneaththe floor deck and extending lengthwise of the outer shell, the outershell, floor deck and keel beams defining a plurality of passagewaysalong the length of the module, winding fiber and impregnating materialon mandrels in a plurality tubular sections defining the plurality ofpassageways, joining the plurality of tubular sections in side-by-siderelationship in an assembly substantially defining in cross section thecross-sectional shape of the module, winding fiber and impregnatingmaterial around the assembly to a preselected thickness for the outershell, and curing the fiber and impregnating material.

DESCRIPTION OF THE DRAWINGS

FIGS. 1a-1e show representative cross sections of bridge structuresillustrative of the invention;

FIG. 2 shows the representative bridge cross section of FIG. 1e inillustration of typical fabrication steps for bridge structuresaccording to the invention;

FIGS. 3a and 3b show two representative joint configurations for the FIG1a-e structures;

FIG. 4 shows a side view in section of a bridge of the invention withrepresentative transitioning structure to buildings; and

FIGS. 5a and 5b illustrate in cross-section two representative columnsupport and saddle structures for anchoring a representative bridge ofthe invention.

DETAILED DESCRIPTION

Referring now to the drawings, FIGS. 1a-e show representative crosssections of substantially axisymmetric bridge structures 11, 13, 15, 17,19 illustrative of the invention. FIG. 2 shows the representative bridgecross section of FIG. 1e in illustration of typical fabrication stepsfor bridge structures according to the invention. As suggested in FIGS.1a-1e, the cross section of the bridge structure may be substantiallyround or oval in shape (FIGS. 1a, 1d) or rectangular in shape (FIGS. 1b,1e), or a combined shape (FIG. 1c). A bridge structure of the inventionmay have any suitable cross section, the invention not consideredlimited by the representative shapes shown in FIGS. 1a-1e, although theselected shape should be amenable to fabrication by winding methodsappropriate for composite fabrication suggested below. The structuresmay have diameters or widths in the range of about 8 to 15 feet, and maybe fabricated in modular sections of lengths limited only by thefabrication method and winding facility used for fabrication. Typicalmaximum modular lengths may be 60 to 70 feet. As is discussed in moredetail below in relation to suggested fabrication and assembly methods,multiple modular sections may be joined together to achieve a longerspan.

Referring now specifically to FIG. 2, the structures of the inventionmay preferably comprise an outer substantially tubular shaped modularshell 21, a floor deck 22, and one or more keel beams 23 extendinglengthwise of structure 19. Keel beams 23 lend substantial lengthwise(axial) bending and buckling strength to structure 19. A ceiling panel(not shown in FIG. 2, but see, e.g., FIGS. 1a, 1c, 1d) may also beincluded if desired. The channels 24 extending lengthwise of structure19 thus defined by the lower side of outer shell 21, deck 22 and beams23 may be conveniently used to enclose heating, electrical, ventilationand air conditioning and other utilities. Likewise, the space above anyceiling panel may be used to enclose lighting, electrical or otherservices. The space in the ceiling area as well as the space defined bydeck 22 and the lower portion of outer shell 21 may be filled with rigidfoam, honeycomb, or balsa wood material to enhance rigidity to the deckand ceiling should heating and electrical utilities not be required.Handrails 25 may be attached to the interior of structure 19 usingmechanical fasteners or adhesives.

Structure 19 may be fabricated utilizing filament winding or towplacement (the term "winding" herein refers to filament winding, towplacement or other method that yields an enclosed shape). FIG. 2 showsschematically a system for filament winding a structure such asstructure 19. The system includes filament winding machine 27, a source28 of filament or tow, and means 29 for applying impregnating material30 to the filament or tow. In the winding operation, structure 19 may bewound on a suitable mandrel comprising an element of winding machine 27at selected filament winding speed and winding angle relative to theaxial direction of structure 19 by drawing filament or tow 32 fromsource 28 through impregnating material 30 and onto the wound structureon the mandrel. In filament winding, the fiber and/or tows are heldunder constant tangential tension during winding. In tow placement, thetows are applied under radial pressure, resulting in tight materialconsolidation. The resulting wound structure 19 may then be cured, andnecessary finishing operations performed on the structure.

It is noted that the wound structure (such as 19) may be fabricated inalternative ways. First, outer modular shell 21 may be wound to anydesired finished thickness consistent with anticipated load levels to becarried by the bridge. Floor deck 22 and keel beams 23 are attachedwithin shell 21 by mechanical or adhesive means. Alternatively, thestructure may be fabricated by winding the structure in sections andassembling the sections to form the finished structure. In thisprocedure, a number of separate sections defined by, for example, outershell 21 and deck 22, and sections defined by deck 22, the lower surfaceof shell 21 and keel beams 23 may be separately wound to partialfinished thickness, assembled together by mechanical or adhesive means,and the assembly wound to finished thickness as suggested in FIG. 2. Ineither structure, the resulting skin could either be monolithic FRP or asandwich of FRP and core material.

Typical filament materials include carbon, graphite, boron, KEVLAR (anaromatic polyamide), glass, aluminum or others as would occur to theskilled artisan practicing the invention. The filaments may beimpregnated with suitable materials such as any thermosetting polymers,thermoplastic polymers, polyimide materials or combinations thereof toform the desired FRP. The structure may be made substantially fireretardant by using glass, carbon or graphite fibers in phenolicpolyimide or furan impregnating material, or other combinations as wouldoccur to the skilled artisan guided by these teachings. Structuralrigidity could be enhanced through the use of sandwich core materialsuch as aluminum or polymeric honeycomb, polymeric foams, carbon foams,plywood or balsa wood.

Other composite fabrication methods may be applicable to the inventionas would occur to the skilled artisan guided by these teachings, such ashand lay-up, pultrusion and vacuum assisted resin transfer molding(VARTM). Hand lay-up involves the placement of resin impregnated fabricor unidirectional tape onto a mold or tool, followed by heat treatmentunder pressure of the tool and plies of fabric to cure the FRP. In thepultrusion method, tows of fibers are pulled through a heated die of thedesired product shape. In the VARTM method, dry fabric or fibers areplaced onto a mold, the whole system is enclosed in a sealed bag, and avacuum is pulled on the bagged part while resin is infused into thefibers or fabric of the part.

Windows may be incorporated into the bridge structure by cuttingopenings in the wound structure and attaching frames in the openings totransfer load and hold the windows in place, or by winding the structurearound specially configured blank tooling inserts to define windowopenings and then attaching frames to hold the windows in place, or byusing window material as the inserts and integrally winding the windowinto the structure. Load requirements on the finished structureprimarily control the filament winding angle and the resulting windowsize, shape and placement.

Thermal insulation may be incorporated into the structure by applying afoam, honeycomb or other rigid insulative material during the windingprocess to produce a multi-layered structure of winding and insulation.The interior walls of the structure may be coated with a fire retardantmaterial or the structure may be wound using fire retardant FRP.

FIGS. 3a and 3b illustrate two ways of joining modules. One end of amodule 31 may be inserted into a flared end 32 of an axially adjacentmodule 33, or a prefabricated coupling 36 may be slipped over the endsof two abutting modules 37,38. Both methods provide a strong stablejoint when adhesive is applied to the joint region before connection.The distance coupling 36 over laps each module 37,38 is preferably atleast one-half the diameter of each module. The distance the flared end32 should slip over module 31 is preferably at least one-half thediameter of module 31.

Multiple modules can be joined at the site by placing the modules andcouplings in-line with each other, applying adhesive to the inside ofthe couplings, and then sliding the modules and coupling together.

Referring now to FIG. 4, a collar coupling 41 or flexible bellowscoupling 43 may be used to transition between buildings and a modularbridge structure 45 and suitable supports such as columns 47 may be usedto provide any needed support between the ends of structure 45. In thecase of use of collar coupling 41, first inserted onto structure 45,and, once the module (structure 45) is in place, the collar is slidagainst the building or through the building opening for permanentsealing attachment utilizing attachment means well known in the buildingart. Sealants may be used to create a water tight coupling at the collarmodule end while not inhibiting expansion movements.

FIGS. 5a and 5b show representative module support arrangements for abridge structure of the invention. Structures 51,52 are supported inrespective saddles 53,54 on one or more columns 55,56. As suggested inFIG. 5b, saddle 54 may be an integral part of structure 52. As shown inFIG. 5a, an optional strap 57 may be used to secure the structure on thesaddle. Saddles 53,54 and columns 55,56 may be configured conventionallyusing suitable material (such as wood, concrete, FRP, or metal) selectedto accommodate the bridge load and design and site peculiarities.

The invention therefore provides a fiber reinforced plastic bridgestructure and fabrication method. It is understood that modifications tothe invention may be made as might occur to one with skill in the fieldof the invention within the scope of the appended claims. Allembodiments contemplated hereunder that achieve the objects of theinvention have therefore not been shown in complete detail. Otherembodiments may be developed without departing from the spirit of theinvention or from the scope of the appended claims.

I claim:
 1. A method for fabricating a fiber reinforced composite bridgemodule, comprising the steps of:(a) providing a source of fiber and asource of impregnating material; (b) selecting a cross-sectional shapefor the bridge module defined by an outer substantially tubular shapedshell having a top side and a bottom side, and a floor deck near saidbottom side, said outer shell and floor deck defining a plurality ofpassageways along the length of said module; (c) winding on mandrelssaid fiber and impregnating material in a plurality tubular sectionsdefining said plurality of passageways; (d) joining said plurality oftubular sections in side-by-side relationship in an assemblysubstantially defining a cross section said cross-sectional shape ofsaid module; (e) winding said fiber and impregnating material aroundsaid assembly to a preselected thickness of said outer shell; and (f)curing said fiber and impregnating material.
 2. The method of claim 1wherein said module has a width up to about fifteen feet and a length ofup to about seventy feet.
 3. The method of claim 1 wherein said fibercomprises a material selected from the group consisting of carbon,graphite, boron, an aromatic polyamide, glass, and aluminum.
 4. Themethod of claim 1 wherein said impregnating material is selected fromthe group consisting of thermosetting polymers, thermoplastic polymers,and polyimide material.
 5. The method of claim 1 wherein saidimpregnating material is phenolic polyimide or furan.
 6. The method ofclaim 1 further comprising the step of incorporating thermal insulationinto said outer shell during the step of winding said fiber andimpregnating material around said assembly to produce a multi-layeredstructure of winding and insulation in said outer shell.
 7. A method forfabricating a fiber reinforced composite bridge module, comprising thesteps of:(a) providing a source of fiber and a source of impregnatingmaterial; (b) selecting a cross-sectional shape for the bridge moduledefined by an outer substantially tubular shaped shell having a top sideand a bottom side, and a floor deck near said bottom side; (c) windingsaid fiber and impregnating material to separately form said outer shelland said floor deck; (d) curing said fiber and impregnating material ineach of said outer shell and floor deck; and (e) joining said outershell and floor deck in an assembly defining in cross section saidcross-sectional shape of said module.
 8. The method of claim 7 whereinsaid module has a width up to about fifteen feet and a length of up toabout seventy feet.
 9. The method of claim 7 wherein said fibercomprises a material selected from the group consisting of carbon,graphite, boron, an aromatic polyamide, glass, and aluminum.
 10. Themethod of claim 7 wherein said impregnating material is a thermosettingresin.
 11. The method of claim 7 wherein said impregnating material isphenolic polyimide or furan.
 12. The method of claim 7 furthercomprising the step of incorporating thermal insulation into said outershell during the step of winding said fiber and impregnating material toform said outer shell to produce a multi-layered structure of windingand insulation in said outer shell.